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TIMING, LOCATION AND POPULATION CHARACTERISTICS

OF SPAWNING MONTANA ARCTIC GRAYLING

(THYMALLUS ARCTICUS MONTANUS [MILNER])

IN THE BIG HOLE RIVER DRAINAGE, 1989

STATE DOCUMENTS COLLECTION

December 1990

n iff \f by

OCT .; 1991 ■

MONTANA STATE L(8RARV

1515 E. 6th AVE.
HELENA, MOM TANA 59620

Bradley B. Shepard and Richard A. Oswald

Montana Department of Fish, Wildlife and Parks

1400 South 19th Street

Bozeman, Montana 59715

Funding Provided by:

Montana Department of Fish, Wildlife and Parks

Montana Natural Heritage Program - Nature Conservancy

U.S. Forest Service, Northern Region

MONTANA STATE LIBRARY

e M? 55 M26tLp 1989 c 1 Shepard
?iSoca.ion and population cha,ac,e

3 0864 00067222 3

1990 Grayling Spawning Report

EXECUTIVE SUMMARY

We sampled spawning Montana Arctic grayling (Thymallus
arcticus montanus [Milner]) by electrof ishing within the upper Big
Hole River drainage from April through May 1989. Sample sites
included the main stem Big Hole River from above Wise River up to
Jackson and the lower portions of three tributaries to the river
were sampled from April through May. We describe the temporal and
spatial distribution of spawning grayling, habitat utilized for
spawning, and demographic characteristics of the spawning popula-
tion.

We captured 407 grayling. The first ripe male was captured on
April 21 in Swamp Creek and the first ripe female on April 25 in
the Big Hole River above the Clemow Road above the town of Wisdom.
The numbers of captured ripe females peaked during the period
between April 26 and May 8 with the only spent female captured on
May 8. The numbers of ripe males peaked during the period between
April 24 and May 10. Spawning could not be correlated to river
flows or water temperatures because the USGS gauge did not begin
operating until May 1, 1989. The sex ratio of all captured fish
identified as mature, ripe, or spent was 1.6 males: 1.0 female. A
large portion of age II fish were sexually mature (61%). The
average lengths and weights of ripe males (n = 123) and ripe
females (n = 19) were 11.8 inches and 0.52 pounds and 11.4 inches
and 0.48 pounds, respectively. Grayling spawned primarily within
the main stem Big Hole River from the mouth of the North Fork Big
Hole River upstream to 3 miles above Wisdom, in a few scattered
side channels below the North Fork, and in the lower portions of
Swamp, Big Lake, and Rock creeks.

We found spawning grayling on riffles with clean surface
gravel which appeared "bright" near pool or run habitats, generally
within actively degrading or aggrading side channels or alluvial
gravel fans at the mouth's of tributaries. We captured most
spawning grayling in areas of hydrologic instability where the
channel was actively down-cutting or depositing gravels. Measure-
ments in eleven areas found spawning grayling were usually captured
in sites where water velocities were faster and water depths deeper
than adjacent available areas.

The age composition of the sampled population suggested that
the 1986 year class (which was a strong year class recruited to the
population in 1988) experienced poor survival from the spring of
1988 to the spring of 1989. The 1985 and 1987 year classes were
also poor and the 1990 spawning run will likely be a poor run.
Grayling hatched during 1988 made up a surprisingly good year class
as evident from the high numbers of age I fish captured during the

Page - ii

1990 Grayling Spawning Report

spring of 1989 and, hopefully, this year class will remain strong
and grow to maturity. It is probable that the Big Hole River
grayling population will be dependent upon this 1988 year class.

Of 38 grayling recaptured during spring 1989 sampling, fifteen
were tagged during the same sampling, seventeen were tagged in
1988, one was tagged in 1987, and five tagging locations could not
be determined. Tagging data illustrated that movements between the
lower river near Fishtrap Creek and upper river near Wisdom, and
between the main stem river and its tributaries were occurring.
This tag return information lends additional support to our
observations that at least a segment of the Big Hole River grayling
population uses the entire river above Divide on a seasonal basis.
We believe a portion of the grayling population normally moves to
the upper river (near Wisdom) during the spring, remains in this
area of the river during the summer, before emigrating down river
to winter habitats. Use of the lower portions of at least some
tributaries by Big Hole River grayling was further supported.

Page - iii

1990 Grayling Spawning Report

TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY ii

TABLE OF CONTENTS iv

LIST OF TABLES vi

LIST OF FIGURES vii

ACKNOWLEDGEMENTS viii

INTRODUCTION 1

STUDY SITE DESCRIPTION 1

METHODS 1

FISH COLLECTION 1

SPAWNING HABITAT CHARACTERISTICS . . . . " 7

RESULTS 8

TIMING OF SPAWNING 8

SPAWNING RUN CHARACTERISTICS 9

SPAWNING DISTRIBUTION WITHIN THE DRAINAGE 9

MOVEMENT ASSESSED USING TAG RETURNS 11

CHARACTERISTICS OF SPAWNING HABITAT 14

Visual Characteristics 14

Measured Characteristics 14

DISCUSSION 18

TIMING OF SPAWNING 18

CHARACTERISTICS OF THE SPAWNING RUN 18

DISTRIBUTION OF SPAWNING WITHIN THE DRAINAGE 19

MOVEMENT 19

Page - iv

1990 Grayling Spawning Report

TABLE OF CONTENTS
(continued)

Page

SPAWNING HABITAT CHAPLACTERISTICS 20

LITERATURE CITED 21

Page - v

1990 Grayling Spawning Report

LIST OF TABLES

Page

1. Electrof ishing sampling dates, locations, and approxi-
mate length of sample sections for electrof ishing
sampling of the 1989 spawning Arctic grayling population

in the Big Hole River 4

2. Mean length, length range, and sex ratio information by
age for the portion of the Big Hole River Arctic grayling
spawning run sampled during 1989 9

3. Summary of tag return information for recaptured Arctic
grayling captured during the spring of 1989 13

4. Average depth (ft.), velocities at 0.6 and 0.1 depth
(fps), and surface substrate composition (%) at capture
locations of ripe and mature grayling (USED) and at
adjacent (AVAIL) areas 15

Page - vi

1990 Grayling Spawning Report

LIST OF FIGURES

Page

1. Map of the Big Hole River drainage 2

2. Daily discharge (cfs) and mean, minimum, and maximum
water temperatures in the Big Hole River near Wisdom,
Montana from May through July 1989 3

3. Catch of grayling 8.0 inches and longer in the Big Hole
River and its tributaries by date during 1989 .... 8

4. Length frequency of Arctic grayling captured during the
1989 spawning run by half inch length group 10

5. Growth of grayling in the Big Hole River drainage during
1988-89 estimated from mean lengths at age . . 11

6. Depths at grayling spawner capture sites (USED) compared
to depths at adjacent unused sites (AVAILABLE) for eleven
sites sampled during 1989 16

7. Both 0.6 and 0.1 depth velocities at grayling spawner
capture sites (USED) compared to 0.6 and 0.1 depth
velocities at adjacent unused sites (AVAILABLE) for
eleven sites sampled during 1989 17

Page - vii

1990 Grayling Spawning Report

ACKNOWLEDGEMENTS

The U.S. Forest Service, Montana Natural Heritage Progreun of
The Nature Conservancy, and Montana Department of Fish, Wildlife
and Parks provided funding for this project. The authors would
especially like to thank Dave Genter of the Montana Natural
Heritage Program; Don Bartschi of the U.S. Forest Service, Regional
Office; Ron Prichard, the Beaverhead National Forest's Supervisor;
Dennis Havig and the entire District Staff of the Wisdom Ranger
District; and Larry Peterman and Dick Vincent of the Montana
Department of Fish, Wildlife and Parks for their support and
encouragement. A special thanks to John Snyder, Terry Williams,
Greg Gibbons, and Tim Mosolf for their untiring and cheerful help
in the field. Dave Genter and Chris Hunter reviewed early drafts
of this report, their comments were invaluable and, in most cases,
incorporated into this report.

Any reference to product names are intended to document the
type of equipment used and do not represent a product endorsement.

Page - viii

1990 Grayling Spawning Report

INTRODUCTION

The last riverine (fluvial) native population of Montana
Arctic grayling (Thymallus arcticus montanus [Milner]) in the
contiguous 4 8 United States exists in the upper Big Hole River of
southwestern Montana (Liknes and Gould 1987). Shepard and Oswald
(1989) reported the historic distribution and status of Arctic g-
rayling in the lower 48 United States and discussed the evidence
for a unique Big Hole River fluvial stock. They documented the
past investigations of the Big Hole River grayling population and
the recent declines observed in grayling numbers. They also
reviewed the literature regarding spawning cues and habitat
requirements .

STUDY SITE DESCRIPTION

The study area included the upper Big Hole River drainage up
river from Divide, Montana (Figure 1). Sampling was concentrated
within the main stem Big Hole River from the towns of Wise River
upstream to approximately 5.0 miles above Wisdom and in the lower
portions of its tributaries including Big Lake Creek, Deep Creek,
Sand Hollow Creek, Steel Creek, and Swamp Creek. Unfortunately,
the USGS river flow gauge and water temperature gauge at Wisdom did
not begin operation until May 1, 1989. Consequently, river flow
and water temperature data were unavailable during the entire
sampling of the spawning run. During May, Big Hole River flows and
water temperatures ranged from 36 to 648 cfs and 41 to 61 F,
respectively, using preliminary data supplied by the USGS from a
gauge located at the Highway 43 bridge near Wisdom (Figure 2).

METHODS

FISH COLLECTION

Grayling were captured using either boat mounted electro-
fishing gear (either a Buffalo Drift boat or Coleman Crawdad
outfitted with a 240 watt gas powered generator connected to a
Harvey Leach constructed variable voltage pulsator with mobile
anodes) or a backpack electrof isher (Coeffelt BP-IC) electrof ished
in a downstream direction. Sampling began on April 18 and
continued through May 18 (Table 1). Two crews operated during the
peak of the spawning run. A total of approximately 4 9 miles of
river and 8 miles of tributaries were surveyed during the spawning
season. We restricted our sampling during 1989 to those areas
where we captured grayling during 1988. We placed red plastic
survey flags at most locations where ripe or mature grayling were

Page - 1

1990

1990 Grayling Spawning Report

(cfs)

D 4000
I
S

H 3000

c 2000

1000 -

TEMPERATURE

Daily Mean_^''->

DISCHARGE

Gr Spawn

Max

Min

25
20

I- 15
10

h 6

E
M
P
E
R
A
T

(C)

1 1 1 1 1 II 1 1 1 1 1 1 ii 1 1 1 1 1 1 1 1 II 1 1 1 1 11 1 1 1 1 1 II 1 1 1 1 II 1 1 1 II 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
Apr 1 Apr 16 May 1 May 16 May 31 June 15

Figure 2. Daily discharge (cfs) and mean, minimum, and maximum water
temperatures in the Big Hole River near Wisdom, Montana from
May through July 1989. Preliminary data collected by the
USGS. Timing of grayling spawning cross-hatch bar.

Page - 3

1990 Grayling Spawning Report

captured and noted the approximate distance from these flags into
the channel which was the actual capture site. If we had placed a
survey flag, we noted whether the fish captured at that location
was ripe or mature .

Stunned grayling, rainbow trout, and brook trout were

captured, except as noted on Table 1. For all captured fish,

length was measured to the nearest 0 . 1 inch and weights were
recorded to the nearest 0.01 pound.

Table 1. Electrofishing sampling dates, locations, and approximate
length of sample sections for electrofishing sampling of
the 1989 spawning arctic grayling population in the Big
Hole River.

Date

Location

Section
length (mi)

Comments

4-18-89 Big Hole R. - E channel 2.0
below Wisdom

4-19-89 Big Hole R. - McDowell 5.0
section above Wisdom

4-20-89 Big Hole R. - Wisdom down 5.4
to Cemetery

4-20-89 Swamp Creek - N Fk 2.0
Big Hole Rd to mouth

4-21-89 Big Hole R. - Swamp Ck 0.2
to Sand Hollow Ck

4-24-89 Big Hole R. - McDowell 5.0
section above Wisdom

4-24-89 Big Hole R. - Doolittle 3.5
to Crane Ranch

4-25-89 Big Hole R. - Twin Lake 4.0
Rd to Clemow Rd

4-26-89 Big Hole R. - Wisdom 5.4
section below Wisdom

6 GR - none ripe

1 GR - immat

8 EBT

38 GR - 3 ripe M
36 EBT

9 GR - 2 ripe M
67 EBT, 3 LING

2 GR - 1 ripe M
2 EBT

10 GR - 6 ripe M
10 EBT, 1 RB

13 GR - none ripe
5 EBT

2 GR - 1 ripe M
- 1 ripe F

14 EBT, 2 RB

24 GR - 14 ripe M
- 2 ripe F
20 EBT, 1 RB, 5 LING

Page - 4

1990 Grayling Spawning Report
Table 1. (continued).

Date

Location

Section
length (mi)

Conunents

4-26-89

4-27-89

5-01-89
5-02-89

5-02-89

5-03-89

5-04-89
5-05-89
5-08-89

Big Hole R. - Cemetery
to Doolittle Ck

6.6 57 GR - 17 ripe M

- 3 ripe F
35 EBT

Swamp Ck - N Fk Big Hole 2.0
Rd to mouth

Steel Ck. - Steel Ck Rd
to mouth

Big Hole R. - Steel Ck
mouth to Cemetery

Big Hole R. - Cemetery
down to Doolittle

Deep Ck. - French Ck
down to below Ski Hill
bridge

Big Hole R. - Sportsman
Park down to East Bank

Big Hole R. - Fishtrap
down to Sportsman Park

Big Hole R. - Cemetery
down to Doolittle Ck

5-08-89 Big Hole R. - Wisdom to 5.4
Cemetery

5-09-89 Swamp Ck. - N Fk Big 2.0
Hole Rd to mouth

5-09-89 Big Hole R. - Swamp Ck 0.2
to Sand Hollow Ck

15 GR - 6 ripe M

- 2 ripe F

156 EBT, 10 LING

1.2 5 GR - none ripe
460 EBT, 31 LING

3.4 27 GR - 4 ripe M

- 1 ripe F
34 EBT, 14 LING

6.6 50 GR - 27 ripe M
- 6 ripe F
42 EBT

2.0

No GR
63 EBT,

42 RB, 1 LL

5.0

1 GR -
26 EBT,

immat
27 RB

3.0

15 GR -
58 EBT,

1 ripe F
14 RB, 1 LL

6.6

25 GR -
35 EBT

16 ripe M
1 ripe F

28 GR - 7 ripe M

- 2 ripe F

- 1 spnt F
46 EBT, 2 RB

8 GR - all immat
81 EBT

1 GR - immat

Page - 5

1990 Grayling Spawning Report
Table 1. (continued).

Date

Section
Location length (mi)

Comments

5-09-89

Big Hole R. - Wisdom
down to Cemetery

5.4

32 GR - 4 ripe M
- 1 ripe F
63 EBT

5-10-89

Big Hole R. - Wisdom to
Cemetery

5.4

12 GR - 6 ripe M
31 EBT, 2 LING

5-11-89

Big Hole R. - McDowell
section above Wisdom

5.0

6 GR - 2 ripe M
15 EBT, 1 RB

5-17-89

Big Hole R. - Fishtrap
to Sportsmen Park

3.0

1 GR - immat
28 EBT, 7 RB

5-18-89

Big Lake Ck. - Clemow Rd
down

1.0

33 EBT

Sex and state of maturity (immature; mature, but not ripe;
ripe; or spent) were recorded for all grayling. Sex determination
was based on extrusion of gametes, the ability to feel eggs within
the body cavity, and the shape of the dorsal fins as documented by
Rawson (1950). Ripeness of female grayling was difficult to
determine until immediately prior to and during spawning. It was
difficult to determine if males were spent because sperm could
still be extruded from spent fish.

Scale samples were removed from grayling and scale impressions
were made in acetate. Scale samples were later read for age
determination. Age interpretation from scale samples up to age IV
was believed relatively accurate, while estimation beyond age IV
was suspect. Growth interpreted from scales should be reliable
because scale samples were obtained in the spring during annulus
formation.

Page - 6

1990 Grayling Spawning Report

All grayling and rainbow trout longer than 8.0 inches were
tagged with a "spaghetti-type" numbered anchor tag. Recaptures of
previously tagged fish were noted. Points of capture for grayling
were visually noted and recorded in the field. Recorded informa-
tion included the general habitat type and streambed condition
where fish were captured and the location by river landmark. These
capture locations were later converted to river mile locations
using USGS maps (scale: 1:24,000) and a River Mile index.

SPAWNING HABITAT CHARACTERISTICS

Capture sites of ripe grayling were visually characterized
including habitat type (riffle, pool, etc.) and channel type (main
channel, side channel, braided channel). A survey crew returned to
11 sites where mature and/or ripe grayling were captured to detail
the spawning habitat being utilized. At the point of capture a
transect was run across the channel and water depth and flow at 0.6
and 0.1 of total depth were measured. In addition, streambed
composition was visually estimated by classifying the streambed
into silt (0 to 63 microns), sand (64 microns to 0.08 in), small
gravel (0.09 to 0.25 in), gravel (0.26 to 3.0 in), and cobble (3.1
to 10.0 in) size categories.

Page - 7

1990 Grayling Spavming Report

TIMING OF SPAWNING

RESULTS

A total of 407 grayling were captured. The first ripe male grayling was
captured on April 21 in Swamp Creek downstream from the lower North Fork Road
near Wisdom (Figures 1 and 3). The first identified ripe female grayling was
captured in the Big Hole River on April 25 up river from the Clemow Road above
the town of Wisdom. The numbers of ripe females peaked during the period between
April 26 and May 8 (Figure 3). The numbers of ripe males peaked during the
period between April 24 to May 10. The only spent female was captured on May 8.

N
U
M
B

E
R

F
I

S
H

APR 15

OTHER
EE] SPENT FEMALE
^ RIPE FEMALE
■I RIPE MALE

APR 22

APR 29

DATE

MAY 6

1 — I — I — r
MAY 13

Figure 3. Catch of grayling 8.0 inches and longer in the Big Hole
River and its tributaries by date during 1989. Grayling
were segregated into "ripe male", "ripe female", "spent
female", and "other" categories.

SPAWNING RUN CHARACTERISTICS

Page - 8

1990 Grayling Spawning Report

SPAWNING RUN CHARACTERISTICS

The sex ratio of all fish identified as mature, ripe, or
spent was 1.6 males: 1.0 female, but was 1.2 males: 1.0 female for
those fish aged (Table 2). Length and age frequency information
for mature fish illustrated that a large portion of the age II fish
were sexually mature (Table 2 and Figure 4). The fact that the

Table 2. Mean length, length range, and sex ratio information by
age for the portion of the Big Hole River Arctic grayling spawning
run sampled during 1989.

Age Number Mean length Length range Percent Sex ratio
class sampled (inches) (inches) mature (male: female)

144

4.8

3.8 -

- 6.3

None

8.8

7.3 -

- 10.4

2.0:1.0

11.1

9.9 -

- 12.8

0.9:1.0

12.6

11.7 -

- 13.8

100

1.5:1.0

5 +

13.5

12.9 -

- 14.9

100

1.3:1.0

Total

281

1.2:1.0

sex ratios change between age classes illustrates that not all
female grayling were maturing at age II and that female grayling
may be suffering higher mortality than males after age IV (Table
2). The average length and weight of ripe males (n = 123) was 11.8
inches and 0.52 pounds, respectively. The average length and
weight of ripe females (n = 19) was 11.4 inches and 0.48 pounds,
respectively. The majority of growth in length was attained at by
age III with the fastest growth occurring during the first and
second years of life (Figure 5).

SPAWNING DISTRIBUTION WITHIN THE DRAINAGE

Most captured grayling spawning during 1989 were found within
the main stem Big Hole River between the North Fork of the Big Hole
River upstream to approximately 3.0 miles above the Highway 43

Page - 9

1990 Grayling Spawning Report

■1 RIPE MALES

'■iM

i RIPE FEMALES 1

■ OTHER

6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0

LENGTH CLASS (0.5 inch)

Figure 4. Length frequencies of Arctic grayling captured during the
1989 spawning run (by half inch length group) . Ripe
grayling included all fish identified as either ripe,
mature, or spent.

bridge near the town of Wisdom and in the lower portions (generally from their
mouth upstream one to two miles) of Swamp, Big Lake, and Rock creeks (Figure 1).
Isolated spawning areas were observed in side channels within the main stem Big
Hole River above the Highway 43 bridge near Squaw Creek and between Sawlog and
Fishtrap creeks.

Page - 10

1990 Grayling Spawning Report

16-
14-
12-

LENGTH (in.)

-^ 1989

^— -^

■■•:J:::::^^

10-

P X

n -I

y \ 1 1 1 1

0 ^ 1 1 1 1 1
0 12 3 4 5 +

AGE

Figure 5. Growth of grayling from the Big Hole River
drainage during 1988-89 estimated from mean
lengths at age.

Figure 5. Growth of grayling in the Big Hole River
drainage during 1988-89 estimated from mean
lengths at age.

MOVEMENT ASSESSED USING TAG RETURNS

A total of 42 grayling were recaptured during this sampling.
Of these 42, four were multiple recaptures of tags captured more
than once during 1989, leaving 38 recaptures to identify. Fifteen
of these recaptures were tagged within the same year (1989) and 23
were tagged in previous years (Table 3). Of the 23 tagged in
previous years, seventeen were tagged in 1988, one was tagged in
1987, and five tagging locations could not be determined. Of the

Page - 11

1990 Grayling Spawning Report

seventeen grayling tagged during the spring of 1988 and recaptured
during the spring of 1989, three were tagged near Fishtrap Creek (a
distance of at least 18 river miles), seven were tagged close to
their recapture location, two were tagged between five and ten
miles above their recapture location, and four were tagged between
five and ten miles below their recapture location. One grayling
recaptured on May 9, 1989 was tagged on August 9, 1988
approximately two miles above the recapture location.

A fish recaptured on April 27, 1989 approximately 1.5 miles up
Swamp Creek was initially tagged on April 27, 1988 (exactly one
year earlier) in the main stem Big Hole River near the mouth of the
North Fork Big Hole River (a distance of approximately eight
miles). This female was 12.2 inches and 0.54 pounds when tagged
and 12.5 inches and 0.56 pounds when recaptured a year later.

One grayling was recaptured twice. Once on April 26, 1989 in
the main stem Big Hole River near McVey Creek and again on April
27, 1988 in the Big Hole River near McVey Creek. This fish was
tagged on October 23, 1987 in the main stem Big Hole River near
Fishtrap Creek (the movement from Fishtrap to McVey Creek was 20
miles). This female was 10.8 inches and 0.45 pounds when tagged
and 11.2 inches and 0.42 pounds when recaptured in 1988 and 12.7
inches and 0.58 pounds when recaptured in 1989.

Page - 12

1990 Grayling Report

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Page - 13

1990 Grayling Spawning Report

CHARACTERISTICS OF SPAWNING HABITAT

Visual Characteristics

Ripe grayling usually were found in riffle areas over gravel
which appeared "bright" due to the absence of periphyton and/or
silt and sand sized material on the surface of the streambed.
These riffle areas of "bright" gravel were often associated with
recently created side channels, below beaver dams and irrigation
diversion structures, and/or near mouths' of tributaries where
alluvial gravel fans had formed. Electrof ishers became relatively
efficient at identifying areas where ripe grayling were likely to
be captured by the middle of the spawning season. These areas
could be characterized as being in areas of hydrologic instability,
often in recently cut side channels where a riffle with "bright"
gravel was situated near a pool or run, or over recently deposited
gravels .

Measured Characteristics

Velocity, depth, and substrate composition measurements were
taken across eleven sites where ripe grayling were captured. Ripe
grayling were captured at depths averaging 2.2 feet with
water velocities averaging 1.9 fps at 0 . 6 depth and 1.1 fps at 0 . 1
depth (Table 4). Substrate composition at capture sites averaged
11% silt, 20% sand, 32% small gravel, 31% large gravel, and 6%
cobble (Table 4). Available velocities, depths, and substrate
compositions in adjacent areas were also measured. Available
velocities averaged 1.5 fps at 0.6 depth and 0.9 fps at 0.1 depth
(Table 4). Available depths averaged 1.8 feet. Available
substrate composition averaged 14% silt, 23% sand, 32% small
gravel, 24% large gravel, and 7% cobble. From these measurements
it appears that grayling may select deeper, and possibly, faster

Page ~ 14

1990 Grayling Spawning Report

Table 4. Average depth (ft.), velocities at 0.6 and 0.1 depth
( f ps ) , and surface substrate composition (%) at capture
locations of ripe and mature grayling (USED) and at
adjacent (AVAIL) areas. Sample sizes in parentheses.
Data from 11 capture site locations sampled during the
1989 spawning run.

Velocity ( f ps )

Depth 0.6 0.1
(ft^ depth depth

Surface substrate (%)

Small Large
Silt Sand gravel gravel Cobble

AVAIL 1.8 1.6 0.9 14 23
(84) (76) (72) (80)

USED 2.2 1.9 1.1 11
(28) (28) (27) (28)

water (Figure 6 and 7) for spawning and also select areas over
cleaner (less sand and silt) substrate which contains higher
percentages of large gravel. The stream substrate results tend to
support the supposition (based on limited hollow core data) of
Shepard and Oswald (1989) that grayling may need relatively clean
substrate with a small percentage of fine sediment on the surface
for spawning. These results must be viewed with caution because
there is no way to determine exact spawning locations using
electrof ishing.

Page - 15

1990 Grayling Spawning Report

FREQUENCY

14-
12 -
10
8 -
6 -
4 -
2
0

USED

0.5 1.0 1.5 2.0 2.5

DEPTH (FT)

AVAILABLE

3.5

4.0

Figure 6. Depths at grayling spawner capture sites (USED)
compared to depths at adjacent unused sites
(AVAILABLE) for eleven sites sampled during 1989.

Page - 16

1990 Grayling Spawning Report

0.6 DEPTH

FREQUENCY
7t

0.6

1,0

IS 2.0 2.S

VELOCITY (FT/S)

3.0

FREQUENCY

0.1 DEPTH

VELOCITY (FT/S)

Figure 7. Both 0.6 and 0.1 depth velocities
at grayling spawner capture sites (USED)
compared to 0.6 and 0.1 depth velocities at
adjacent unused sites (AVAILABLE) for eleven
sites sampled during 1989.

Page - 17

1990 Grayling Spawning Report

DISCUSSION

A detailed discussion of Big Hole River grayling spawning
population characteristics and timing, with a comparison to results
from studies on other grayling populations was made in last year's
report (Shepard and Oswald 1989). Only information not presented
previously or interpreted differently from the previous report is
presented below.

TIMING OF SPAWNING

The numbers of ripe females during the 1989 spawning run
peaked during the period between April 26 and May 8. This
corresponds very closely to the period of peak spawning activity
(April 27 to May 10) observed during 1988 (Shepard and Oswald
1989). Unfortunately, during 1989 the USGS gauge at Wisdom was not
operated until May 1, 1989. This late start for gauge information
prevented us from evaluating effects of flow and water temperature
on grayling movement and spawning. MDFWP has alerted the USGS that
we need to have the gauge begin operating April 1 of each year.

CHARACTERISTICS OF THE SPAWNING RUN

The sex ratio of grayling identified as mature, ripe, or spent
was 1.6 males: 1.0 female during 1989. Sex ratios for the Big Hole
grayling spawning population in 1988 was 2.0 males: 1.0 females (see
last year's report [Shepard and Oswald 1989] for a comparison to
other grayling populations).

The growth curve for grayling in the Big Hole system illus-
trates that the majority of growth occurs during their first two
years (Figure 5). The presence of some juveniles in tributaries to
the river and the interpretation of early growth from a few scales
suggests that a small segment of the juvenile population may remain
(rear) for up to two years in tributaries to the river. Growth of
fish captured during the spring of 1989 was slower than for those
captured during the spring of 1988. The drought of 1988 was
probably a major factor which contributed to this reduced fish
growth in the Big Hole River system.

The relatively strong 1986 year class (age 2 fish) that was
seen in 1988 did not appear to carry over to 1989 which provides
further evidence of the stress the 1988 drought put on the grayling
population (Figure 4). Fortunately, it appears the grayling
hatched out during 1988 (1988 year class) contributed to a
relatively strong year class and experienced relatively high
survival through their first year (Figure 4). We are unsure why

Page - 18

1990 Grayling Spawning Report

age II fish experienced poor survival, while age 0 fish experienced
good survival, from the spring of 1988 to the spring of 1989. This
differential survival between age 0 and age II fish warrants
further investigation. We found the numbers of fish age two and
older were very low and it appears that once the age 4 and older
fish die, there will be few mature fish to spawn during 1990 and
1991.

DISTRIBUTION OF SPAWNING WITHIN THE DRAINAGE

The distribution of grayling spawning within the Big Hole
drainage was similar in 1988 and 1989. Areas in the main stem
above the North Fork of the Big Hole River and lower Swamp Creek
were used for spawning. Sample electrof ishing in the portion of
the Big Hole River between Fishtrap Creek and the East Bench BLM
access indicated that rainbow trout were utilizing spawning
habitats where grayling were typically found in the Wisdom portion
of the river. We speculate that rainbow spawners may compete with
grayling spawners and have successfully excluded them from spawning
sites in the lower portion of their range within the Big Hole.

MOVEMENT

The movement patterns observed through recaptures of tagged
fish in the Big Hole suggests that a segment of the riverine Big
Hole grayling population spends the winter in deep pools in the
portion of the river down river from the Wisdom area as far as the
Divide dam and perhaps in some tributaries with deep pools or areas
of groundwater recharge. During the spring, some of the mature
grayling from the lower river move up river and spawn in the
portion of the river from the mouth of the North Fork up to
immediately above Wisdom, and in the lower portions of Swamp,
Steel, Big Lake, Rock, and Sand Hollow creeks.

From tag return data it is difficult to determine if the gray-
ling population within the upper Big Hole River consists of one or
more discrete stocks. It is apparent that some grayling in the Big
Hole system move between the lower and upper river seasonally for
spawning and, perhaps, to seek over winter habitat. Seasonal
movement patterns indicate that some grayling adults move into
spawning areas located in the upper river above the North Fork from
the lower river near Fishtrap Creek. We are unsure if these fish
move immediately down river after spawning, or if they remain in
the upper river over the summer before moving back down during the
fall. Past information indicated mature-sized grayling spent the
entire summer within the upper portion of the drainage in the
Wisdom area as documented by summer and fall electrof ishing (Liknes
1978; Oswald 1984; Oswald 1986). There may be two discrete life-
Page - 19

1990 Grayling Spawning Report

history patterns followed by Big Hole River grayling. One segment
of the population may move seasonally between the lower and upper
river and one segment may remain in the upper and/or lower river
year round.

Tag return evidence from one tagged fish also suggests that
Big Hole River grayling use the lower portion of Swamp Creek for
spawning. We infer from movement exhibited by this fish that it is
likely that grayling populations in the lower portions of Steel,
Swamp, Big, and Rock creeks are probably very similar, if not a
direct subset, of the Big Hole River population. We believe it is
likely that grayling populations within the lower portions of Big
Hole River tributaries receive enough genetic transfer with Big
Hole River grayling that grayling in these tributaries should be
considered as members of the Big Hole River grayling population.

We are unsure of the status of isolated grayling populations
inhabiting the upper portions of tributaries such as Mussigbrod
Creek, upper Wise River, and Wyman and Bobcat creeks. We believe

that these populations originated with outmigranta from lake

populations, but are unsure how long they have been genetically
isolated and the result of potential genetic isolation and
adaption.

SPAWNING HABITAT CHARACTERISTICS

We found ripe Big Hole grayling over gravel that was very
clean on the surface located in riffle areas in close proximity to
pool or deep run habitats. This observation made in 1988 was
further substantiated in 1989 by classifying substrate composition.
Ripe grayling also appeared to seek areas where water velocities
were faster and water was deeper than was generally available
(Figures 6 and 7).

Page - 20

1990 Grayling Spawning Report

LITERATURE CITED

Liknes, G. A. 1981. The fluvial Arctic grayling (Thymallus

arcticus) of the upper Big Hole River Drainage, Montana. M.S.
Thesis, Montana State University, Bozeman, Montana.

Liknes, G. A., and W. R. Gould. 1987. The distribution, habitat
and population characteristics of fluvial arctic grayling
(Thymallus arcticus) in Montana. Northwest Science 61:122-
129.

Oswald, R. A. 1984. Inventory and survey of the waters of the
Big Hole and Ruby River drainages. Job Progress Report,
Fed-ral Aid in Fish and Wildlife Restoration Acts, Project
Number F-9-R-31 and 32, Job Number 1-b, Bozeman, Montana.

Oswald, R. A. 1986. Inventory and survey of the waters of the
Big Hole, Beaverhead and Ruby River drainages. Job Progress
Report, Federal Aid in Fish and Wildlife Restoration Acts,
Project Number F-9-R-34, Job Number 1-b, Bozeman, Montana.

Rawson, D. S. 1950. The grayling (Thymallus sianifer) in
northern Saskatchewan. Canadian Fish Culturist 6:3-10.

Shepard, B. B. 1986. Beaverhead National Forest and Montana

Department of Fish, Wildlife and Parks Cooperative Fishery
Program. First Annual Report covering the period August 15 to
December 31, 1985. Beaverhead National Forest, Dillon,
Montana.

Shepard, B. B. 1987. Beaverhead National Forest fisheries:

Second annual report covering the period January to December
1986. Cooperative study between the Beaverhead National
Forest and the Montana Department of Fish, Wildlife and Parks,
Beaverhead National Forest, Dillon, Montana.

Shepard, B.B. and R.A. Oswald. 1989. Timing, location, and
population characteristics of spawning Montana Arctic grayling
(Thymallus arcticus montanus [Milner]) in the Big Hole River
drainage, 1988. Montana Department of Fish, Wildlife and
Parks, Bozeman, Montana.

Page - 21

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